1. Field of the Invention
The present invention relates to an ink jet recording apparatus for a printer or a facsimile machine, and to an ink jet head used for the ink jet recording apparatus, a nozzle plate used for the ink jet head, an apparatus for manufacturing the nozzle plate and a method for manufacturing the nozzle plate.
2. Related Background Art
An ink jet recording apparatus is known that records characters and images on a recording medium by employing an ink jet head wherein a plurality of ink chambers, made of a piezoelectric material for which a poling process has been performed, are arranged in parallel, and electrodes are mounted on two inner walls of the individual ink chambers, and wherein the piezoelectric material is deflected by selectively transmitting a drive pulse signal to these electrodes, and to thus discharge ink from a plurality of nozzle openings that communicate with the ink chambers. This ink jet recording apparatus moves a carriage, on which the ink jet head is mounted, in the main scanning direction relative to the recording medium, and discharges ink from the nozzles of the ink jet head to print a dot pattern in a predetermined area. When one main scanning has been completed, the ink jet recording apparatus moves the recording medium a predetermined distance in the sub-scanning direction, and repeats the above described operation to print all the desired area.
For such an ink jet head, since an ink chamber shares a side wall with adjacent ink chambers, the discharge of ink in the ink chamber is affected by the driving condition of the peripheral ink chambers. Further, since the pressure in the ink chamber fluctuates during driving, the preceding state, i.e., whether the ink chamber has been driven, also affects the discharge of the ink in the ink chamber.
Assume that to print a linear line an ink jet head is moved from the left to the right, and discharges ink from nozzles (discharge portions) of the predetermined contiguous portion of the ink jet head. In this case, as shown in FIG. 10A, a line would be printed that is curved at the ends. FIG. 10A is a diagram showing ink droplets that landed at this time, and FIG. 10B is a specific diagram showing the nozzle plate used for printing this line. Such a line, one curved at the ends, is printed because the ink discharge speed is low for nozzles located near portions whereat ink is not discharged, and ink droplets do not land at targeted discharge positions. That is, the difference in the discharge speed causes a shift in the landing time for ink droplets on a recording medium, i.e., the shifting of the dot positions, and accordingly, the printing quality is deteriorated. Specifically, of the nozzle openings 28 arranged in a discharge portion, the ink discharge speed for the nozzle opening 28a located nearest the non-discharge portion is 70 to 80% that of the ink discharge speed for the nozzle opening 28x located in the middle of the discharge portion.
As described above, the factor responsible for the reduction in the speed of the ink discharged from the nozzle located near the non-discharge portion may be that there is a small pressure change in the ink chamber consonant with the pertinent nozzle. That is, for this type of ink jet head chip, ink chambers that share a side wall are formed in parallel by cutting a single piezoelectric ceramic plate. Therefore, since one specific ink chamber receives pressure vibrations from adjacent ink chambers, the internal pressure vibration in the specific ink chamber is affected. And when only one adjacent ink chamber is driven, the pressure fluctuation in the specific ink chamber is reduced, compared with when all the peripheral ink chambers are driven. This trend is noticeable immediately after a printing operation is started that employs ink chambers that had not previously been driven. And when ruled lines and characters are printed, the curving of straight lines is outstanding.
To address the difference in the speed of ink droplets discharged from an ink chamber, an ink jet recording head driving method is proposed. According to this method, it is first determined whether ink chambers adjacent to a specific ink chamber were driven before being currently driven, and in accordance with the determination results, a wave having a different drive pulse is applied.
However, according to this method, in order to determine, at each ink discharge time, whether the ink chambers adjacent to the specific ink chamber have been driven, a special dedicated circuit and a controller are required, and the manufacturing cost is increased.